Contemporary aircraft engines include electric machines, or generator systems, which utilize a running aircraft engine in a generator mode to provide electrical energy to power systems and components on the aircraft. Some aircraft engines can further include starter/generator (S/G) systems, which act as a motor to start an aircraft engine, and as a generator to provide electrical energy to power systems on the aircraft after the engine is running. Motors and generators can be wet cavity systems, wherein a cavity housing the rotor and stator is exposed to liquid coolant, or dry cavity systems, wherein the cavity is not exposed to liquid coolant. Dry cavity systems can also utilize liquid coolant in one or more contained cooling systems, but they are still considered dry cavity so long as the cavity is not exposed to liquid coolant. Both contemporary types of wet or dry cavity systems have respective advantages. For example, dry cavity systems generally have less losses, higher efficiency, higher reliability, less required maintenance, and attitude independence over wet cavity systems. In contrast, the power density of a wet cavity electric machine can be considerably higher than that of a dry cavity electric machine due to its higher cooling effectiveness.
The operating requirements or the operating environment of a generator system can increase the cooling requirements for either a wet cavity or dry cavity system. For example, generator systems proximate to the high temperature environment of a turbine engine can further include an external cooling jacket surrounding the stator or generator, whereby the cooling jacket exposes the outer surface of the stator to coolant traversing a cooling jacket. The addition of cooling systems typically increases the costs, complexity, and adds to the weight and size requirements of the generator system.